1. Field of the Invention
The present invention relates to a magnetic recording medium that has a low level of head wear as well as little head contamination after running.
2. Description of the Related Art
Magnetic recording media have been widely used as sound recording tapes, video tapes, computer tapes, disks, etc. The density of magnetic recording media has been increasing year by year, and the recording wavelength has been decreasing. Moreover, recording systems from analogue systems to digital systems have been studied.
In particular, a magnetic recording medium in which a ferromagnetic metal powder comprising mainly Fe is coated together with a binder on a non-magnetic support currently dominates the field of media for video for broadcasting and data recording because of its excellent cost performance. In drives for video for broadcasting and data recording, higher capacity together with higher speed of the magnetic recording medium relative to the magnetic head, the so-called xe2x80x98higher transfer ratexe2x80x99, are being developed. In order to achieve a higher capacity, it is necessary to increase the recording density, and a magnetic recording medium having excellent electromagnetic conversion characteristics is required. In systems in which a high capacity and a high transfer rate are realized, particularly in VTRs for broadcasting, an expensive head assembly is installed. Since the relative speed between head and tape is high in accordance with the high transfer rate, wear of the magnetic head seriously affects the maintenance and the running costs of the above-mentioned systems, and there is therefore an intense demand for a magnetic recording medium that has a low level of head wear, thereby increasing the head lifespan.
The present invention has been carried out in view of the above-mentioned circumstances.
It is an object of the present invention to provide a magnetic recording medium that has a low level of head wear and is excellent in terms of head contamination and still frame durability. A specific object is to provide an excellent magnetic recording medium for a system in which there is a high relative speed between tape and head and a large area of tape is used per unit time, the magnetic recording medium having low wear of the magnetic head and at the same time little head contamination.
Usually, when the head wear is reduced, the head contamination characteristics are impaired. With regard to means for reducing the head wear, there are known methods such as a method in which the type of an abrasive in the magnetic layer is changed to one having a lower abrasive power or the amount thereof is reduced, a method in which the composition of an oxide film on the ferromagnetic metal powder is adjusted, and a method in which the kneading intensity during preparation of a magnetic liquid is optimized. However, these methods cannot fully overcome the above-mentioned trade-off relationship, and the above-mentioned demand cannot be met.
As a result of an intensive investigation by the present inventors in order to solve the mutually contradictory problems of head wear and head contamination, it has been found that the object can be accomplished by a magnetic recording medium comprising a non-magnetic support, and a magnetic layer formed on the support and comprising mainly a binder resin and a ferromagnetic metal powder comprising mainly Fe, said magnetic layer comprising an abrasive and a lubricant, the abrasive present on the surface of the magnetic layer satisfying the relationship:
0.01xe2x89xa6H15/H10xe2x89xa60.3 
and the magnetic recording medium having a surface lubricant index of 3 to 11, where H10 denotes the number of particles per unit area having a height less than 10 nm (particles/xcexcm2), and H15 denotes the number of particles per unit area having a height equal to or greater than 15 nm (particles/xcexcm2).
The above-mentioned object, other objects, features, and advantages of the invention will become clear from the following description.